200 



NA TURE 



[July 2, 1908 



RECENT WORK WITH THE SPECTRO- 

 HELIOGRAPH. 



PROFS. HALE AND ELLER^L\^■, of Mount Wil- 

 son Solar Observatory, California, enjoying- the 

 advantages of a climate almost unrivalled and an 

 instrumental equipment of the highest class, have 

 already given to the world scientific results worthy 

 even of such a combination. In connection with their 

 more recent work we have received several photo- 

 graphs, one of which is reproduced here. .Among 

 the photographs are discs of the sun in the light of 

 iron (^ 4045), and an interesting comparison of the 



Negative of a portion of the solar surface in Ha light, 



solar surface as seen through the calcium line (H-.) 

 and the hydrogen line (H6), showing in a striking 

 manner that the regions of maximum radiation of 

 calcium light are regions of absence of hydrogen 

 radiation. 



In obtaining photographs of hydrogen flocculi, the 

 hvdrogen line H5 has chiefly been used. In March, 

 190S, it was found possible, by the use of the new 

 "' Pan-iso " plates of Wallace, to secure photographs 

 of the sun with Ho. The comparison of the resulting 

 photographs with those taken in HS showed bright 

 flocculi peculiar to Ha, and small dark areas appear- 



NO. 2018, VOL. 78] 



ing solely in H5. L'sing the various hydrogen lines for 

 the photography of the chromosphere and prominences, 

 the greatest intensity and extent were found in the 

 photographs taken with Ha. These qualities de- 

 creased through the hydrogen lines H/8 and H7 until in 

 Hfi only the brightest parts of the prominences were 

 shown. Considering the integrated hydrogen light of 

 the disc, these facts indicate an increase of relative 

 intensity in the Ha line, or, as put in the letter ac- 

 companying the photographs, show that " hydrogen 

 appears in contiguous regions on the sun under some 

 of the peculiar conditions which produce differences in 

 the relative intensities of its lines observed in nebula.- 

 and in stars having spectra of the 

 ^^'olf-Rayet and other special 

 types. " 



The feature of special interest in 

 the photograph reproduced (which 

 is a neg^ative of part of the 

 solar surface taken in Ho) is 

 the strong suggestion of the 

 existence of vortex systems 

 surrounding the spots. The 

 specially extensive and well- 

 marked phenomena near the centre 

 of the illustration, it is suggested, 

 show that " the prominences sur- 

 rounding this area . . . are swayed 

 towards the centre, and their apoear- 

 ance strongly suggests the effect of 

 a great whirl rotating clockwise " 

 (i.e. N.W.S.E.). 



It is to be noticed that the dark 

 hvdrogen flocculi appear bright on 

 the negative as reproduced. The 

 photograph was taken on .\pril 30, 

 iqoS, 5h. 6m. p.m.. Pacific standard 

 time. .-V direct photograph secured 

 on the same date shows a group of 

 small spots near the centre of this 

 region, while a plate in H, licht 

 shows a calcium flocculus lying 

 above the spots. Neither of the 

 above photographs affords any evi- 

 dence of whirl. The remarkable 

 features shown in the illustration 

 are thus apparently confined to the 

 higher regions of the solar atmo- 

 sphere, and are selectively photo- 

 graphed by making use of the 

 special qualities of the hydrogen 

 line Ha, though the general 

 appearance calls to mind the torn 

 edges of a sun-spot as drawn bv 

 Langley. 



The picturing by spectrohelio- 

 graphic means of the distribution of 

 radiating matter at various solar 

 evels is already well known. The 

 photograph reproduced illustrates 

 what "can be done in quite a new 

 wav bv using this valuable means 

 of acquiring information about solar circulation. 



It may be pointed out in passing that the appear- 

 ances in the great whirl might be explained equally 

 well, or perhaps even beiter. from the fining away 

 outward.'; of the hydrogen flocculi, as an anti-clock- 

 wise whirl outwards from the centre. Occasionally 

 on photographs in " K " light taken at South Ken- 

 sington, some suggestions of extensive whirl systems 

 surrounding centres of activity are observed. 



The relation of the photography of high-level 

 hydrogen flocculi to the recent work of Hale and 

 .■\dams on the rotational velocities in various latitudes 



